Approximating X

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JohnWalkiewicz2J
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Approximating X

Postby JohnWalkiewicz2J » Mon Mar 09, 2020 10:59 pm

When solving ICE tables or a equilibrium concentration for a R/P, for what value of Q/K do you approximate x, so you don't have to use the quadratic formula. Thnx in advance!

EthanPham_1G
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Joined: Sat Jul 20, 2019 12:17 am

Re: Approximating X

Postby EthanPham_1G » Mon Mar 09, 2020 11:07 pm

If the K value is smaller than 10^-4 then you can approximate the x value. You can double check this by using the 5% rule. If the percent ionization is 5% or less then it is ok to approximate the x value.

Sartaj Bal 1J
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Re: Approximating X

Postby Sartaj Bal 1J » Wed Mar 11, 2020 9:52 am

Minor detail, but in response to the above, I believe it's okay to approximate if the K value is 10^-4 or smaller.

Izzie Capra 2E
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Re: Approximating X

Postby Izzie Capra 2E » Wed Mar 11, 2020 10:49 am

Make sure you always check using the 5% ionization rule when approximating, there are some odd cases where the K value is incredibly small but there can be a discrepancy of greater than 5%. In this case, you would have to use the quadratic formula.

William Chan 1D
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Re: Approximating X

Postby William Chan 1D » Wed Mar 11, 2020 10:13 pm

The general rule is that, if k is smaller than 10^-4, then it should be safe to assume that the change in concentration is negligible and that x can be ignored. Of course, you can always check that the difference is less than 5% to make sure.

Manav Govil 1B
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Re: Approximating X

Postby Manav Govil 1B » Thu Mar 12, 2020 10:07 am

This is a helpful link if you're confused!

https://www.khanacademy.org/science/che ... r-small-kc

Anna Heckler 2C
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Re: Approximating X

Postby Anna Heckler 2C » Thu Mar 12, 2020 10:29 am

If the k value is very small (i.e. less than 10^-4) then you can approximate.

Tanmay Singhal 1H
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Re: Approximating X

Postby Tanmay Singhal 1H » Thu Mar 12, 2020 12:51 pm

if x is very small. i believe less than 5%

ramiro_romero
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Re: Approximating X

Postby ramiro_romero » Thu Mar 12, 2020 10:24 pm

I specifically remember Lavelle mentioning in one of his lectures that if the value for K is less than (10^-3), then it is okay to approximate for x. Usually, just consider your initial moles of reactant and that the x value should leave no significant difference after subtracted from the moles of reactant (When approximated).

Jessa Maheras 4F
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Joined: Fri Aug 02, 2019 12:16 am

Re: Approximating X

Postby Jessa Maheras 4F » Sat Mar 14, 2020 6:27 pm

Manav Govil 1B wrote:This is a helpful link if you're confused!

https://www.khanacademy.org/science/che ... r-small-kc

Thank you this link is very helpful!

Emily Lo 1J
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Joined: Thu Sep 19, 2019 12:16 am

Re: Approximating X

Postby Emily Lo 1J » Mon Mar 16, 2020 2:31 pm

If your K value is less than 1.0*10^-3, then you can assume that the x value will not greatly effect the values in your equation. So if the K value is that small, you can assume that the x value in the denominator is 0.

Jarrett Peyrefitte 2K
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Joined: Sat Aug 24, 2019 12:16 am

Re: Approximating X

Postby Jarrett Peyrefitte 2K » Mon Mar 16, 2020 2:51 pm

ff the K value is smaller than 5% aka 10^-4, then x can be approximated

Ayushi2011
Posts: 101
Joined: Wed Feb 27, 2019 12:17 am

Re: Approximating X

Postby Ayushi2011 » Mon Mar 16, 2020 6:06 pm

Use the 5% rule, if X is less than that then we can approximate.

Gurmukhi Bevli 4G
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Joined: Wed Nov 14, 2018 12:20 am

Re: Approximating X

Postby Gurmukhi Bevli 4G » Wed Mar 18, 2020 1:17 am

You can approximate the x value provided K<10^-4 (or smaller), and as already stated, you can cross check using the 5% ionization rule.


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